The first and very important thing, is to you talk with her.

Talk with her in a very calm way, ask her, she needs to feel heard. Kindness could work.

So she can open up and then be a bit more receptive about you saying the things you see she is not doing very good.

But that, talk a lot with her. If she is too erratic and doesnt listen, sorry, nothing you can do, but try to talk all things with her.